Comforters and pacifiers in the past have been manufactured from a variety of different materials and in a variety of different designs. In the past, only natural latex was available for this purpose whereas, more recently, a greater preference has been shown for silicone rubber.
The advantages of silicone rubber lie above all in its excellent ageing behavior, in its ease of handling for cleaning and sterilization, in its high transparency for better control of cleanness, its ease of processing injection moulding machines and the like.
Hitherto, comforters of the natural latex or silicone rubber have normally been made in a hollow mould with wall thicknesses of up to about 2 mm, for which purpose a material having a Shore A hardness of 30 to 60 was used. Larger wall thicknesses were not selected because otherwise the comforter would have felt too hard and would not have been taken by the infant. Solid comforters of this material were undesirable for the same reasons.
However, since the force generally required to destroy a comforter increases proportionally with the wall thickness, it is obvious that stable and hence thick-walled comforters should be made for safety reasons. However, this is not possible with available materials because otherwise the comforters obtained would not be sufficiently soft and elastic.